password authentication failed for user postgres

Hi,

1. I have added listen_addresses = '*' ; in postgresql.conf

2. And have made the following changes to pg_hba.conf

local DATABASE USER METHOD
local samegroup all password
host DATABASE USER CIDR-ADDRESS METHOD [OPTION]
host all all 0.0.0.0/0 md5
hostssl all all 0.0.0.0/0 md5

3. Have restarted the server

4. I can login to the server as user postgres.

But while trying to createuser I get the following message :
'createuser: could not connect to database postgres: FATAL :
password authentication failed for user "postgres"

This is on Redhat running Plesk also.

I am new to Linux as well as PostgreSQL. Help would be much appreciated.

Thanks
Viv